Pneumatic pumps and electric pumps can be controlled to generate periodic pulses of pressurized liquid or gas. Prior art systems for doing this typically require control circuits which periodically energize pumps or which control switching valves to generate a desired sequence of pressurized pulses. The complicated systems of the prior art are expensive to make and maintain.
Pressurized air flows are used in innumerable applications; two very limited and distinctive examples include cans of compressed air that can be used to clean dust from surfaces, and fans that are used to provide a concentrated and pressurized air flow for lawn equipment such as leaf blowers. In the example of a leaf blower, it is well known that in the use of conventional equipment such as hand-held rakes or motor driven sweepers, obstacles such as cars parked in parking spaces make it necessary to leave parts of the area uncleaned, whereas, if the same area is cleaned with a leaf blower is it possible to blow away the rubbish underneath the parked cars, thereby increasing the efficiency, save time and improve the result. U.S. Pat. No. 7,185,393 illustrates one configuration of a leaf blower that typically includes at least a fan assembly to generate a substantially continuous flow of pressurized air of constant velocity and a tubular duct or nozzle which concentrates the flow so it can be manipulated or aimed by the operator to direct the air flow toward the surface to be cleaned of debris. Users often move the leaf blower laterally in a sweeping motion to move debris from a surface to be cleaned, but moving the leaf blower's duct or nozzle in that lateral, sweeping motion causes operator fatigue. Similarly, in the example of a compressed air container (e.g., as packaged in the Dust Off™ product) users must move the entire compressed air source to produce a sweeping motion to achieve the desired results.
To eliminate the need to move the entire source of the air flow in order to get a sweeping motion of pressurized air for use in cleaning surfaces, sweeping jet fluidic oscillators have been developed for a variety of uses. The use of such oscillators for defrosting and defogging operations on automobile windshields, for example, is disclosed in Kakei et al. U.S. Pat. Nos. 3,832,939 and 3,745,906, in Stouffer U.S. Pat. No. 4,250,799 (and divisions thereof), and in Stouffer et al, U.S. Pat. No. 4,644,854. In Kakei et al., several forms of sweeping jet oscillators for defrost purposes are disclosed, one of which includes a fluidic oscillator in which a pair of crossed feedback pipes receives portions of air issuing from an outlet downstream of an oscillator throat portion and returns the air to a pair of control ports. In the Stouffer '799 patent, a vibrating reed oscillator is utilized which significantly reduces the amount of space required, but in this device the movement of a weighted end of the vibrating reed through the jet or air stream creates a swishing sound noticeable to passengers in the close confines of an automobile.
In Stouffer et al, U.S. Pat. No. 4,644,854, the volumetric space occupied by a fluidic oscillator for the defrost system in an automobile is reduced by making the fluidic oscillator relatively short. This oscillator is of the type having a power nozzle, a pair of control ports immediately adjacent to and downstream of the power nozzle, and a continuous inertance loop interconnecting the control ports. Flow straighteners are preferably utilized just at the manifolding of the oscillator to the automobile duct work to thereby reduce the length of ducting to the power nozzle and thereby assure a more uniform and symmetrical velocity profile of the air stream entering the power nozzle. Fluid inertance is a measure of the pressure required to accelerate a mass of fluid in a passageway and thus is associated with flow through a tube or passage and is a function of the length and cross-sectional area thereof. Since the fluidic oscillator utilized is more sensitive to the inertance loop's cross-sectional area than to its length, that is, the fluidic flow is sensitive to abrupt changes in cross-section, particularly sudden reductions in the cross-sectional area of the continuous inertance loop, an important feature of that invention is the avoidance of abrupt changes in direction or cross-sectional area of fluid flow in the continuous inertance loop.
The use of electromagnets to regulate control port valving for air flow switching purposes in a power nozzle has been suggested for use in cars but this invites unnecessary complexity and requires a fluid logic element of at least 5W in length, where W is the width of the power nozzle, to get adequate sweeping angles. Fluidic oscillators based on a continuous passage or loop interconnecting the pair of control ports of the fluidic element are known in the art, as disclosed in Van Nostrand's Scientific Encyclopedia (6th Edition) page 1235, for example. In addition, Izumi et al. U.S. Pat. Nos. 4,416,192, 4,407,186 and 4,393,898 disclose use of fluidics with electromagnetic control in directional control of air in automobiles.
U.S. Pat. No. 6,767,331, which discloses a massaging apparatus and thus is only of background interest to the present invention, illustrates an inflatable bladder connected to a structure incorporating a fluidic switch for generating a time-varying bladder inflation flow of fluid, where the pressure is “recovered” from the bladder in a fluidic circuit having an output port that is open to the atmosphere as well as to a vent. The '331 patent does not describe a way of delivering a continuously pulsed supply of a fluid to an output, but, nevertheless, is incorporated herein in its entirety by reference.
Although the above-described prior art illustrates that the production of oscillating fluid flow in relatively small systems is known, there is a need for an economical, inexpensive and reliable system and method for generating an oscillating or a pulsed flow of pressurized gas which is applicable to large and robust equipment such as lawn and cleaning equipment, to overcome the problems of the prior art.